An imaging apparatus is known which, for flash imaging, fires a preflash, and detects reflected light from an object to determine an amount of main-flashing light. Imaging apparatus mainly use a CCD (Charge Coupled Device) image sensor as their image pickup device. Recently, amid the growing trend toward a higher density of pixels on image pickup devices, a CMOS image sensor is drawing attention as a new type of image pickup device. The CMOS image sensor has advantages such as random access to and high-speed reading of pixel signals, high sensitivity, low power consumption, and the like.
However, in a conventional imaging apparatus using a CMOS image sensor, exposure operation and reading operation are performed differently for each pixel, and when a preflash is fired, preflash effects are given only to a part of the image pickup device, posing a problem of difficulty in determining the amount of main-flashing light accurately enough. In order to overcome this problem, an apparatus has been provided which applies a sufficiently long preflash exposure time (see, e.g., Patent Document 1 (Japanese Patent Application Publication No. 2000-196951).